Pretty Little Liars by Sara Shepard

Alison and her friends lead privileged lives in a small town in Philadelphia. When Ali, the unquestioned leader of their group, disappears , her friends are distraught. But they also feel tiny twinges of relief that all the secrets they had shared with Ali are now safe. Soon, however, their seemingly perfect world seems about to unravel as mysterious text messages are received that could only have come from someone who knew what Ali knew. The author maintains a high level of tension throughout the story, which remains unresolved at the end of this first book in the series. The characters are not well differentiated at the beginning of the story, but gradually develop as the story progresses , revealing each to be quite unpleasant in her own way. The story alternates between individual characters’ stories, before bringing the group together at the end. The reader is very tempted to read on as the plot finishes with one chilling question